How to delete photos on iphone?

When I first got my iPhone 4, I synced itunes with it, and I had a ton of pictures on iTunes I didn't know were there. Their original spot was on my Picasa program. Somehow they got on iTunes and all of them went to the iPhone. So how do I get them off there? They take up so much room that I can only shoot a couple of pictures and then the "no more space" message comes up on the iPhone. But it doesn't said anything on iPhoto on how delete unwanted pics, either in photos or iPhoto. Do I delete them from iTunes or is there a way to delete them from the phone?

Added (1). Yeah, Mr. Condescension (Ray). I didn't say delete photos in camera roll. I said synced photos on iPhotos or just the Photos folder. So what it sounds like is that yes, I can delete from the camera roll, and I can't delete other photos which came from the computer on my phone. I have to delete the ones that came from the computer, on the computer itself, right? With an empty folder. Ok, got it. Ray, you said everything but sheeesh!

Don't listen to Ray, he/she is only telling you how to delete photos you took with your iPhone. To delete synced photos with iTunes, sync your iPhone photos again with an empty folder and the photos will be gone.

Either delete or move the photos on your computer, or after clicking your phone while synced in itunes, click the 'photos' button and uncheck the boc, the click sync